“People in our study, like the population at large, differed in the strategies they use to make economic decisions. What sort of strategy people tended to use could be predicted, surprisingly, by how their brain responded to rewards: if there were large responses to monetary reward in a brain area called the ventral striatum, that person tended to simplify decision problems to only consider winning or losing,” said Scott Huettel, senior author of the study.

“Using studies like this to build a better understanding of how our brains represent our decision strategies may someday allow researchers to use someone’s personal traits - say, an adolescent with high impulsivity, but ongoing depression - to predict the decisions that he or she will make.

“This could lead to many real-world benefits: designing more effective interventions or creating more useful educational material,” he added.

In the study, the researchers scanned 23 participants, and observed real-time changes in brain function as they evaluated complex multi-outcome lotteries.

“Our goal was to come up with a risky decision task that would both discriminate between alternative models of choice and represent something that often happens when people allocate scarce resources to make a risky choice more attractive. It was also nice that the task is complex enough to relate to ‘real-world’ decisions but simple enough to be studied using functional MRI,” said Dr. John W. Payne, the Joseph J. Ruvane, Jr. Professor of Business.

And the results revealed that the brain regions classically associated with “rational” processing, particularly the lateral prefrontal cortex, were most active when subjects used a simplifying strategy inconsistent with traditional rational-choice models.

“This result suggests that it was the type of computation that the participants were doing at any given time that activates a brain region, not whether the thought process is rational or irrational,” said lead author Vinod Venkatraman, from the Department of Psychology and Neuroscience at Duke.

“(The finding) argues strongly against the commonly held notion that there are ‘rational’ and ‘irrational’ parts of the brain,’” added Huettel.

The study also showed that the medial prefrontal region of the brain shapes moment-to-moment changes in the strategies people use to make decisions.

“We all make some decisions opposite to our usual tendencies. When we do so, this brain region comes online and alters activation in other choice-related regions,” said Huettel.